Many characteristics of Phelan-McDermid syndrome — an autism-linked disorder arising from abnormalities at the tip of chromosome 22q13 — change as individuals age, reports a study published in January inHuman Genetics1.
People with the syndrome showa wide variety of symptoms, including developmental delay, speech delay, intellectual disability, low muscle tone and, frequently, autism. Mutations in theSHANK3gene, which is linked to autism, are associated withmany of the neurological traitsof the syndrome.
Only about 600 people worldwide are diagnosed with Phelan-McDermid syndrome. A few studies have suggested that the disorder’s features maychange with ageand may include aprogressive loss of skills. However, given the syndrome’s rarity andrelatively recent recognition, the frequency of those changes was unclear.
In the new study, the researchers examined 201 individuals diagnosed with the syndrome and analyzed the results by age. Participants older than 18 years tend to have fewer behavioral problems and better developmental abilities, and fewer of them show theunusual physical featuresassociated with the disorder: full or puffy eyelids, large or fleshy hands, low muscle tone, lax ligaments and overly mobile joints.
However, more individuals in the older age groups reported seizures and diagnoses of autism. This may be because of neurological deterioration over time or because they have had more time to receive a diagnosis. Trauma, infection and other triggers may also be involved.
Seizures affect 11 percent of children younger than 5 years but 60 percent of adults. A higher proportion of adults also have abnormal reflexes, connective tissue inflammation and fluid retention in lymph nodes.
When the researchers analyzed the 22q13 abnormalities in 120 participants, they found that 89 percent had lost the tip of the chromosome, 2 percent had lost an inner section and 11 percent carry both duplications and deletions. The study confirmed previous findings thatthe larger the deletion, the more severe the symptoms.The researchers also found that seizures are more common in individuals who inherited the affected chromosome from their mother....